Parallel path, downdraft gasifier apparatus and method

ABSTRACT

A method for using a downdraft gasifier comprising a housing and a refractory stack contained within the housing. The refractory stack may comprise various sections. Apertures in the sections may be aligned to form multiple columnar cavities. Each columnar cavity may comprise an individual oxidation zone. The method of use may include the steps of placing a feedstock into an upper portion of the refractory stack, measuring the temperature of each columnar cavity, and adjusting the flow of oxygen to a particular columnar cavity to maintain the temperature of the particular columnar cavity within a particular range.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/948,950 filed Jul. 10, 2007.

BACKGROUND

1. The Field of the Invention

This invention relates to fuel generation and, more particularly, tonovel systems and methods for gasification of municipal solid waste andother feedstocks.

2. The Background Art

Manufactured gas, or synthesis gas (syn-gas) as it is more often calledtoday, comprises the unburned gasses (carbon monoxide and hydrogen gas)created by incomplete combustion of an organic raw material.Gasification (the process of generating manufactured gas) was discoveredindependently in both France and England. By 1850, gasification of coalhad developed to where much of London was lit with manufactured gas,“town gas,” or “coal gas” as it was called. By 1920, many towns andcities throughout the United States supplied manufactured gas to theirresidents through local “gasworks.”

Following 1930, as natural gas pipelines began to proliferate, low-costnatural gas displaced manufactured gas. The gasification industry waslargely abandoned and forgotten. However, beginning with the oil embargoof the 1970's, there has been an almost continual increase in the costof fuel. Accordingly, what is needed today is an efficient system,process, and gasifier that can receive a wide variety of inputs andefficiently produce a clean fuel.

BRIEF SUMMARY OF THE INVENTION

In view of the foregoing, in accordance with the invention as embodiedand broadly described herein, a method and apparatus are disclosed inone embodiment of the present invention as including a gasifier system.In selected embodiments, a gasifier in accordance with the presentinvention may include a housing comprising a base, a lower sectionresting on and extending upward from the base, an intermediate sectionresting on and extending upward from the lower section, and an uppersection resting on and extending upward from the intermediate section.The lower section may include a gas outlet and a waste outlet. The uppersection may include a feedstock inlet.

In operation, feedstock may enter a gasifier through the feedstock inletand travel down through the gasifier toward the waste outlet. A gasifiermay include four zones that function in unison to simultaneously processthe feedstock and generate clean syn-gas. These zones are the dryingzone, tar-formation zone, oxidation zone, and reduction zone.

The drying zone may largely be contained within the upper section of agasifier. As the feedstock is stored within the upper section, heatradiating up from a lower, oxidation zone may drive off the residualmoisture as water vapor. The water vapor may be contained within thegasifier and participate in chemical reactions in the reduction zonewhen carbon reacts with the water vapor to generate carbon monoxide andhydrogen (H₂), the desired outputs.

The temperature within the tar-formation zone may be higher than thatwithin the drying zone. In the tar-formation zone, the feedstock may beheated without oxygen to produce oil, tar, char, and charcoal. Theseproducts may provide a ready supply of carbon for the chemical reactionsthat later occur in the reduction zone.

In the oxidation zone, all or part of the volatile materials may beoxidized to generate the heat for the chemical reactions of the process.As feedstock passes out of the oxidation zone, approximately 20% to 30%of the organic material may have been oxidized and the oxygen istypically consumed. Accordingly, there is typically no flame in thesucceeding, reduction zone. Some combustible gases may be generated inthe oxidation zone.

In the reduction zone, the hot gases generated in the oxidation zone mayreact with the carbonaceous material generated in the tar-formation zoneto convert most of the feedstock to syn-gas. During these reactions thesensible heat or heats of the chemical reactions are converted intochemical energy for the syn-gas. This, being endothermic, may result incooling of the mass to below 800° C. This may effectively stop thechemical processes and no further syn-gas is typically formedthereafter.

In selected embodiments, a gasifier may include an enclosed top. Theenclosed top may stop all or some portion of the atmospheric nitrogenfrom entering a gasifier and generating undesirable compounds. Also, theenclosed top may assist in maintaining the desired temperatures withinthe gasifier.

In certain embodiments, a refractory stack may contain and define thetar-formation, oxidation, and reduction zones. A refractory stack may behoused within the intermediate section of a gasifier and include aplurality of sections. The sections may be formed of a heat resistantmaterial. For example, they may be formed of ceramic or refractory.Accordingly, a refractory stack may improve the heat retention,durability, and life span of a gasifier.

The number of sections in a refractory stack may vary betweenembodiments. In one embodiment, a refractory stack may include fivesections, namely, a lower manifold, a lower intermediate section, amiddle intermediate section, an upper intermediate section, and an uppermanifold. The various sections may be stacked one on top of the other.The interior of the upper manifold may contain and define thetar-formation zone. The interior of the lower manifold may contain anddefine the reduction zone.

A shaft may extend from top to bottom through a gasifier. One or moremotors may urge rotation of the shaft about a vertical axis. In selectedembodiments, a gasifier may include a mixing blade connected to rotatewith the shaft. As the shaft rotates, the mixing blade may mix thecontents of the upper section and upper manifold. This mixing mayimprove the distribution of heat rising from the oxidation zone, therebyimproving the drying effect. In selected embodiments, the mixing blademay scrape the contents of the upper manifold away from an interiorsurface thereof, removing any dead or stagnant zones.

Certain sections of a refractory stack may include multiple aperturesextending vertically therethrough. For example, in one embodiment, thelower intermediate, middle intermediate, upper intermediate, and uppermanifold section may each include multiple apertures extendingvertically therethrough. These apertures may be aligned between thevarious sections to form multiple columnar cavities. Each columnarcavity may extend from the upper manifold to the lower manifold, placingthe upper manifold in communication with the lower manifold.

Each columnar cavity may act as an independent oxidation zone and have adedicated heater, dedicated gas ports, and dedicated temperaturesensors. These heaters, ports, and sensors may be positioned within orproximate the apertures defining the columnar cavities. Thus, thenarrowness of the cavities and the positioning of the heaters, ports,and sensors may support individual, rapid, and precise control of theenvironment within each columnar cavity.

In selected embodiments, the various apertures aligning to form thecolumnar cavities may not be exactly cylindrical. For example, theapertures in selected sections may be somewhat conical in shape,converging when viewed with respect to the downward flow of thefeedstock. Apertures so configured may create one or more lips oroverhangs within the columnar cavities. Tucked on the underside of suchoverhangs may be grooves. These grooves may extend the circumference ofthe columnar cavities. Certain grooves may be used to distribute gas(e.g., oxygen) around a circumference of a columnar cavity. Othergrooves may house and protect a heater. Accordingly, a heater may extendcircumferentially around a columnar cavity. A heater may provide greatercontrol in initiating and automating the gasification process.Additionally, a heater may reduce the amount of time required to bring agasifier into optimal production.

In certain embodiments, a grate may be positioned within a gasifier toform the bottom boundary of the reduction zone. A grate may bepositioned proximate the underside of a lower manifold. A lower manifoldmay include an aperture extending vertically therethrough. The aperturemay have an undulating perimeter. A plurality of balls may be supportedby the grate and held by the grate within the aperture of the lowermanifold.

A grate may be connected to rotate with a shaft, which may result inrotation of the balls. Because an aperture having an undulatingperimeter laterally contains the balls, relative rotation between theballs and the aperture may result in agitation or mixing of the balls.The resultant bed of moving and mixing balls may provide a semipermeable barrier, permitting syn-gas and small particles to work theirway through, while blocking the passage of larger particles. Thus, onlyfeedstock that has been sufficiently oxidized and reduced down may exitthrough the bed.

In certain embodiments, a gasifier may include one or more wiper bladespositioned within the reduction zone. A wiper blade may be connected torotate with the shaft. Accordingly, as the shaft rotates, so may one ormore wiper blades. A wiper blade may urge the contents of the lowersection toward the waste outlet.

A gasifier system in accordance with the present invention may include acontrol system. A control system may provide computer-based monitoringand control of selected subsystems of a gasifier system. The subsystemscontrolled by a control system may largely be divided into two classes,namely feedback systems and implementation systems. Through the feedbacksystems, a control system may learn what is happening within thegasifier or other components of the gasifier system. Through theimplementation systems, a control system may effect changes to theoperation of the gasifier system, sound an alarm, or the like.

An extensive sensor suite may form the backbone of a control system'sfeedback systems. By monitoring various sensors such as temperaturesensors, pressure sensors, flow meters, and the like, a control systemmay learn what is happening within a gasifier. A control system then mayissue appropriate commands to one or more implementation systems such asa heater suite, gas-delivery system, and the like. For example, acontrol system may instruct a gas-delivery system to adjust the flow ofgas (e.g., oxygen, oxygen enriched air, air) to a particular columnarcavity. The control system may increase the flow to raise thetemperature within the columnar cavity, decrease the flow to lower thetemperature within the columnar cavity, or the like to maintain thetemperature of the columnar cavity within a particular range.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the present invention will become more fullyapparent from the following description and appended claims, taken inconjunction with the accompanying drawings. Understanding that thesedrawings depict only typical embodiments of the invention and are,therefore, not to be considered limiting of its scope, the inventionwill be described with additional specificity and detail through use ofthe accompanying drawings in which:

FIG. 1 is a schematic block diagram of an overall system and materialflow in accordance with the present invention;

FIG. 2 is a schematic block diagram of a system and method for using theoutputs of a gasifier in accordance with the present invention;

FIG. 3 is a front, perspective view of one embodiment of a gasifiersystem in accordance with the present invention;

FIG. 4 is a back, perspective view of the gasifier system of FIG. 3;

FIG. 5 is a schematic block diagram of a control system in accordancewith the present invention;

FIG. 6 is a schematic block diagram of the various systems andcomponents that may be included in a control system in accordance withthe present invention;

FIG. 7 is a side, cross-sectional view of one embodiment of a gasifierin accordance with the present invention;

FIG. 8 is a side, cross-sectional view of the intermediate section ofthe gasifier of FIG. 7;

FIG. 9 is a perspective view of one embodiment of an upper section of agasifier in accordance with the present invention;

FIG. 10 is a perspective view of one embodiment of an intermediatesection of a gasifier in accordance with the present invention;

FIG. 11 is a perspective view of one embodiment of an aperture cover forthe intermediate section of FIG. 10;

FIG. 12 is a perspective view of one embodiment of a base and lowersection of a gasifier in accordance with the present invention;

FIG. 13 is a perspective view of one embodiment of a top of a gasifierin accordance with the present invention;

FIG. 14 is a perspective view of one embodiment of a bottom of agasifier in accordance with the present invention;

FIG. 15 is a perspective view of one embodiment of a mixing blade inaccordance with the present invention;

FIG. 16 is a top, perspective view of one embodiment of a grate andgrate support in accordance with the present invention;

FIG. 17 is a bottom, perspective view of the grate and grate support ofFIG. 16;

FIG. 18 is a top, perspective view of one embodiment of an uppermanifold of a refractory stack in accordance with the present invention;

FIG. 19 is a bottom, perspective view of the upper manifold of FIG. 18;

FIG. 20 is a top, perspective view of one embodiment of an intermediatesection of a refractory stack in accordance with the present invention;

FIG. 21 is a bottom, perspective view of the intermediate section ofFIG. 20;

FIG. 22 is a top, perspective view of one embodiment of a lowerintermediate section of a refractory stack in accordance with thepresent invention;

FIG. 23 is a bottom, perspective view of the lower intermediate sectionof FIG. 22;

FIG. 24 is a top, perspective view of one embodiment of a lower manifoldof a refractory stack in accordance with the present invention; and

FIG. 25 is a bottom, perspective view of the lower manifold of FIG. 24.

DETAILED DESCRIPTION OF SELECTED EMBODIMENTS

It will be readily understood that the components of the presentinvention, as generally described and illustrated in the drawingsherein, could be arranged and designed in a wide variety of differentconfigurations. Thus, the following more detailed description of theembodiments of the system and method of the present invention, asrepresented in the drawings, is not intended to limit the scope of theinvention, as claimed, but is merely representative of variousembodiments of the invention. The illustrated embodiments of theinvention will be best understood by reference to the drawings, whereinlike parts are designated by like numerals throughout.

Referring to FIG. 1, every year, large quantities of municipal solidwaste (MSW) are collected for disposal. While most of the materialsfound within MSW can be recycled in some manner, the costs of recyclingthe different materials can vary greatly. It is currently feasible torecycle only a portion of the MSW generated. Accordingly, largequantities of MSW are being deposited in landfills each year.

In selected embodiments, systems and methods in accordance with thepresent invention may support use of an entire MSW stream, or somesubset thereof. This may virtually eliminate the need for new or everexpanding landfills. In so doing, systems and methods in accordance withthe present invention may reduce ground water pollution, eliminate odorproblems, and limit the amount of methane released into the atmosphere.With the systems and methods of the present invention, waste may beregarded as a valuable resource.

In certain embodiments, the base components of a system 10 in accordancewith the present invention may be a preprocessor 12 and a gasifier 14. Apreprocessor 12 may receive a feedstock 16 and convert it to a formacceptable to a gasifier 14. A gasifier 14 may receive a pre-processedfeedstock and convert it to a gaseous fuel (e.g., syn-gas). The gaseousfuel may then be used as is or converted to more useful fuels orproducts.

A feedstock 16 in accordance with the present invention may be orinclude materials such as tires 18, used motor oil 20, sewage sludge 22,MSW 24, agricultural waste 26, coal fines 28, petroleum sludge 30, orsome other 32 material such as landfill gas, natural gas, and the like.A preprocessor 12 may receive the feedstock 16 and grind 34, separate36, dry 38, pelletize 40, or otherwise 42 process the feedstock 16 toprepare it for a gasifier 14.

A preprocessor 12 may also enhance 44 a feedstock. For example, coal,coal fines, or some other carbon source may be added to a feedstock 16to enhance 44 the gasification thereof. Additionally, one or morepollutant absorbent binders (e.g., zeolite, dolomite) may be added tothe feedstock 16. The amount of the various binders added may vary,depending on the nature of the feedstock and the pollutants associatedtherewith. As the feedstock is gasified, the binders may react with andtrap chemicals such as sulphur, chlorine, and the like that may beharmful if released into the environment. The tied up pollutantcompounds may leave a gasifier 14 looking like glassy sand. This glassysand may be used as filler by a block plant 48.

The particular functions performed by a preprocessor 12 or as part of apreprocessing step may vary depending on the nature of the feedstock 16.For example, in one exemplary embodiment, the primary ingredient of afeedstock 16 may be unsorted MSW 24. As the MSW 24 is received, largeitems such as appliances, bicycles, engine blocks, etc. may be removed(e.g., by hand) and sold 46 to scrap metal dealers. A preprocessor 12may include a flail mill to break up garbage bags and the like containedwith the MSW 24. The preprocessor 12 may also include a magnet to removefree ferrous metals from the MSW 24.

The preprocessor 12 may also include a grinder to grind 34 the MSW 24.For example, the MSW 24 may pass through a slow turning, size-reductionsheer (e.g., a sheer of 600 horsepower or larger). Accordingly, apreprocessor 12 may grind up furniture, carpet, towels, barrels, andalmost anything else that may be contained within the MSW 24. Thepreprocessor 12 may reduce everything to pieces as small as desired(e.g., no larger than six inches in length).

The preprocessor 12 may be programmed to take protective action uponencountering abnormalities within the MSW 24. For example, if a large,hard, nonmagnetic object (e.g., an aluminum engine block) enters apreprocessor 12 or some component thereof (e.g., a grinder), thepreprocessor 12 may reverse itself one or more times, shut down, soundan alarm, take some other protective action, or the like. The offendingitem may then be removed (e.g., manually) and the preprocessor 12 maycontinue its operation.

Continuing with the exemplary embodiment, the ground MSW 24 may then beconveyed through a magnetic and eddy current separation process. Thisprocess may collect additional ferrous metals freed in the grindingprocess and repel aluminum, brass, and other metals out of the conveyedMSW 24. Accordingly, a high percentage of the saleable metals may beremoved and separated. These metals may be sold 46 to scrap metaldealers.

The remaining MSW 24 may be ground down even further (e.g., to one halfinch in length or smaller). This additional grinding 34 may free suchitems as nails, paper clips, and staples, and the like. The preprocessor12 may include an air classifier. The air classifier may separate 36 andremove the dirt, rocks, glass, remaining metals, and the like from theMSW 24, leaving the gasifiable portion of the MSW 24 stream. Materialssuch as dirt, rocks, glass, and the like may be used as filler by ablock plant 48. For example, the dirt, rocks, and glass may be combinedwith the glassy sand produced by the binders and be bound with ageo-polymer binder to make a strong, concrete-like material. Thismaterial may be used to form building blocks, power poles, highwaydividers, and the like.

Coal, coal fines, or some other carbon source may be added to thegasifiable portion of the MSW 24. Also, one or more pollutant absorbentbinders may be added. The resulting composition may be mixed andpelletized. The pellets may provide the fuel for a gasifier 14 inaccordance with the present invention.

In selected embodiments, the pellets produced by a preprocessor 12 mayhave no more than about 30% moisture content. This may improve theefficiency of the gasification process. Accordingly, if the feedstock 16includes significant quantities of sewage sludge 22, a preprocessor 12may expend significant energy in drying 38 the sludge. Conversely, ifthe feedstock 16 is primarily MSW 24, a preprocessor 12 may expendsignificant energy in grinding 34 and separating 36.

In certain applications, it may be desirable to mix various feedstocks16 to improve the efficiency of a system 10 in accordance with thepresent invention. For example, a city may produce large quantities ofsewage digester sludge 22 and MSW 24. The sludge 22 and MSW 24 may bemixed to form a feedstock 16. In such mixtures, lowering the percentageof sludge 22 may improve the efficiency of the system 10. It is believedthat the increased percentage of MSW 24 may lower the overall moisturecontent of the mixture and, therefore, require less energy to dry thefeedstock 16 to the desired moisture level (e.g., 25% to 30% moisture)prior to pelletizing.

In general, it is undesirable to let MSW 24 and certain other feedstocks16 accumulate, waiting to be processed. Accordingly, a system 10 maysupport rapid swapping in and out of components or equipment modules(e.g., preprocessors 12, gasifiers 14, and the like). For example, asystem 10 or selected components thereof may include quick connects anddisconnects for conduits, electrical wiring, and the like. A system 10or selected components thereof may be mounted on skids to facilitaterapid manipulation thereof within a production facility. Also, a plantmay feature back-up modules in each of the required processes. When onecomponent or equipment module is removed for repair or service, anotherequivalent module may be inserted in its place. Accordingly, down timeand the accumulation associated therewith may be minimized oreliminated.

The flow rate of MSW 24 collection may vary for seasonal and otherreasons. Accordingly, a system 10 in accordance with the presentinvention may include one or more balers. A baler may bale and wrap theexcess MSW 24 during days of higher flow rate. These wrapped bales maybe waterproof and odorless. They may be stacked as necessary, to beretrieved, passed through a preprocessor 12, and gasified on days oflower flow rate. This could be months after the MSW 24 was collected andbaled.

Inside a gasifier 14, a pre-processed feedstock 16 may undergo partialoxidation to produce synthesis gas or “syn-gas.” The syn-gas producedmay primarily comprise hydrogen and carbon monoxide. Hydrogen and carbonmonoxide are primary building blocks for many fuels and chemicals.Moreover, syn-gas itself may be a clean burning fuel suitable for use induel-fuel diesel engines, gas turbines, steam boilers, and the like. Inselected embodiments, the syn-gas produced by a gasifier 14 inaccordance with the present invention may be so clean (e.g., free frompollutants) that it does not require hot-gas cleanup

In certain embodiments, the syn-gas generated by a gasifier 14 inaccordance with the present invention may range from about 300 BTU percubic foot (2670 kilocalories per cubic meter) to about 700 BTU percubic foot (6230 kilocalories per cubic meter). The specific BTU contentmay depend on the desired output. For example, a cleaner gas for fuelproduction may have about 300 BTU per cubic foot (2670 kilocalories percubic meter) and be produced in greater quantities, while a gas to beburned in the generation of electricity may be about 700 BTU per cubicfoot (6230 kilocalories per cubic meter) or above and be produced inlesser quantities.

Once the syn-gas has been generated, it may be used in a number of ways.For example, the syn-gas may be sold to syn-gas consumers 50. Suchcustomers 50 may use the syn-gas as fuel for generating electricity 52,a feedstock for generating other chemicals 54, fuel for heating purposes56, or as something else 58. Alternatively, syn-gas may be passed to asynthesizer 60 to be converted to dimethyl ether (DME).

In selected embodiments, the various components of a system 10 inaccordance with the present invention may be modular. Accordingly, asystem 10 may produce syn-gas for multiple uses or in multiple forms andmay switch to meet immediate needs. For example, during peak demandduring the day, a system 10 may direct all or a significant portion ofthe syn-gas produced to an on-site electric power generation system 52.During times of lower demand, the syn-gas may be passed to a synthesizer60 and converted to DME.

DME has many viable applications 62. It may be used as a propellant 64in hair spray, spray paint, and the like. It is generally considered tobe safer to breathe than other propellants. DME may be used as a coolant66 within refrigeration systems. DME may also be used as a domestic fuel68 (e.g., a substitute for propane), a municipal fuel 70 (e.g., asubstitute for natural gas), and a clean burning diesel fuel 72 with acetane value greater than fifty-five. DME diesel fuel is a gas atstandard temperatures and pressures. However, it can be liquefied at asignificantly lower pressure than fuels like propane. Additionally, likesyn-gas, DME may be used as a fuel for generating electrical power 74, afeedstock in generating other chemicals 75, or as something else 78.

In selected embodiments, DME may be further processed to obtain otherdesired outputs. For example, DME may be passed through a catalyticconversion 80 to generate a sulphur-free fuel 82. Alternatively, DME maybe passed through a catalytic reformation 84 to generate hydrogen fuelcells 86 or purified syn-gas 88, which itself may be used as a fuel forgenerating electrical power 90, a feedstock in generating otherchemicals 92, etc.

A system 10 in accordance with the present invention may support fieldinstallations. For example, there are natural gas wells capable ofproducing significant quantities of natural gas that are not currentlybeing utilized. This is largely due to economics. The quantities ofnatural gas simply cannot justify the cost of connecting the wells to apipeline for collection and transport of that natural gas. Accordingly,the wells are “stranded” and left dormant.

In selected embodiments, systems 10 in accordance with the presentinvention may be assembled at the sites of such wells. Each such system10 may then receive natural gas as a feedstock 16. This feedstock 16 mayrequire little or no preprocessing and may be passed directly input intoa gasifier 14. A process in accordance with the present invention maythen be followed until the natural gas is converted to DME, jet fuel,diesel, gasoline, or the like for transport to market by vehicle. Byconverting the natural gas to a more compact fuel, the value of thatfuel mayjustify the costs of the system 10 and the transport of the fuelto market.

Referring to FIG. 2, in selected embodiments, a DME synthesizer 60 mayconvert syn-gas to DME in a catalytic process. In one embodiment, theconversion may be achieved using a co-catalyst system including amethanol synthesis catalyst and a dehydration catalyst. In such aprocess, syn-gas may be converted to methanol, followed instantly by thedehydration of the methanol to yield DME.

Prior to being converted to DME, syn-gas may be stored 98 andconditioned 100 as desired or necessary. To initiate the conversion, thesyn-gas may be compressed 102 (e.g., to about 40 atmospheres (4040kilopascals)) before being passed to a catalytic converter 104. The twocatalytic reactions typically require only a fraction of a second tooccur and are highly exothermic. Accordingly, timely heat removal mayprevent the catalytic surfaces from coking up and deactivating.

In certain embodiments in accordance with the present invention, acatalytic converter 104 may comprise a cyclone reactor 104. For example,a catalytic converter 104 may be a cyclone reactor 104 as disclosed inInternational Publication No. WO 2005/090272 A1, which is herebyincorporated by reference. In such embodiments, small granular solidcatalysts may be carried in an oil slurry. Syn-gas may be bubbledthrough the slurry as it moves rapidly through a reactor 104. The heatof the catalytic reactions may be transferred to the slurry. Once theslurry exits the reactor 104, it may enter a heat exchanger 106 and theheat of the catalytic reactions may be removed.

The process of passing syn-gas through a catalytic converter 104 may beiterative. For example, in one embodiment, a single pass through acatalytic converter 104 may convert a certain portion of the syn-gas toDME and generate a certain amount of heat. The DME, which may be aliquid at the elevated pressure, may be separated from the syn-gas andpassed to a pressurized storage container 108. The syn-gas may be passedagain through the catalytic converter 104. Meanwhile, the slurry mayreturn to the catalytic converter 104 from the heat exchanger. This maybe repeated one or more times (e.g., three times).

Alternatively, multiple (e.g., three) catalytic converters 104 may bearranged in series. Accordingly, the syn-gas exiting a first converter104 may be the input to a second converter 104, and so forth. Eachconverter 104 may be connected to a single, common heat exchanger 106 orto a separate heat exchanger 106. In such an embodiment, all but about15% of the syn-gas may be converted into DME.

Once the desired portion or percentage of the syn-gas has been convertedto DME, any residual syn-gas may be used as desired or necessary. In oneembodiment, the residual syn-gas may be a clean, burnable gas.Accordingly, it may be applied to any suitable use. In certainembodiments, the residual syn-gas may be used as fuel for a boiler 110.The boiler 110 may generate steam for driving a turbine 112. The turbine112 may be used to generate electricity, drive a compressor, or thelike. For example, in certain embodiments, the power output by a turbine112 may be used to compress 102 the syn-gas, run a preprocessor 12, andthe like. Alternatively, the residual syn-gas may be used in anIntegrated Gasification Combined Cycle (IGCC).

In selected embodiments, one or more heat exchangers 106 may use theheat extracted from the slurry to heat steam. This heated steam may alsobe passed to the turbine 112. Also, heat may be extracted from agasifier 14 (e.g., from cooling the syn-gas after it exits a gasifier14) and passed to a turbine 112. In certain embodiments, all of aportion of the syn-gas produced by a gasifier 14 may be used in an IGCC.Thus, the overall efficiency of a system 10 in accordance with thepresent invention may be increased in a variety of ways.

Once generated, DME may be used, sold, or converted into other products.For example, in certain embodiments of a system and method in accordancewith the present invention, DME may be passed to a fuel synthesizer 114to be catalytically converted into jet fuel, diesel fuel, and gasoline.In selected embodiments, a fuel synthesizer 114 may decompress 116(e.g., to about 2 atmospheres (202 kilopascals)) and heat 118 (e.g., toabout 400° C.) the DME. The synthesizer 114 may then pass the DMEthrough a reactor 120 to convert the DME to lower olefins. In selectedembodiments, the reactor 120 may be a fluidized bed reactor 120. Thesynthesizer 114 may then compress 122 (e.g., to about 50 atmospheres(5050 kilopascals)) the lower olefins.

A fuel synthesizer 114 may include a catalytic converter 124 foreffecting oligomerization of the lower olefins to produce liquid fuel.In selected embodiments, a catalytic converter 124 may be a cyclonereactor 124 as disclosed in International Publication No. WO 2005/090272A1. A catalytic converter 124 may operate in conjunction with a heatexchanger 126 and in an iterative manner, as described hereinabove forthe catalytic converter 104 and heat exchanger 106 of a DME synthesizer60.

Once generated, the liquid fuel may be decompressed 128 and passed to afractionation tower 130. Energy extracted in the decompression process128 may be used to compress 122 DME before it enters a catalyticconverter 124. Within a fractionation tower 130, the liquid fuel may bedivided into about 49% sulfur-free, synthetic jet fuel, 40% sulfur-free,liquid, synthetic diesel fuel and 11% synthetic gasoline of aboutninety-two octane. The conversion rate between DME and liquid fuel maybe about 51%. Thus, each liter of liquid fuel may have close to doublethe BTU content of DME. Moreover, each liter of liquid fuel may haveclose to double the wholesale value of DME.

Referring to FIGS. 3 and 4, a gasifier system 138 may include a gasifier14 and one or more systems supporting operation of the gasifier 14. Inselected embodiments, a gasifier system 138 may include a feed system140. A feed system 140 may include a hopper 142 for receiving andstoring feedstock 16 (e.g., pre-processed feedstock). A hopper 142 maybe mounted directly onto the top of a gasifier 14. Accordingly, a hopper142 may feed feedstock 16 directly into a gasifier 14 under the impetusof gravity. Such an arrangement may simplify and compact the system 138.

In other embodiments, a conveyor system 144 may transport feedstock 16from a hopper 142 to a gasifier 14. In certain embodiments, a conveyorsystem 144 may include a motor 146, a conduit 148, and an augerpositioned within the conduit 148. The conduit 148 may extend from thehopper 142 to the gasifier 14. The motor 146 may urge rotation of theauger within the conduit 148, thereby propelling feedstock 16 from oneend of the conduit 148 (e.g., the end near the hopper 142) to the other(e.g., the end near the gasifier 14).

In selected embodiments, a feed system 140 may be placed under vacuum.This may reduce the amount of nitrogen entering a gasifier 14, therebyfacilitating production of a clean syn-gas. This may be done byconnecting and positioning a vacuum pump 150 to evacuate air from theconduit 148 of the feed system 140. In one embodiment, the vacuum pump150 may operate continuously and reduce, by some percentage, the amountof air within the conduit 148. In such an arrangement, the feedstock 16within the hopper 142 and conduit 148 may provide a barrier tobackfilling air (e.g., air entering the system 140 from the surroundingsin an effort to resolve the pressure differential caused by the vacuumpump 150). While not perfect, the barrier may permit at least a partialvacuum to be maintained in the feed system 140.

Alternatively, multiple gates may be included within the feed system 140to seal it and permit evacuation thereof. The gates may be positionedand operated such that feedstock 16 may be moved (e.g., in batches)through the conduit 148 without exposing the gasifier 14 to ambient air.

A gasifier 14 in accordance with the present invention may include ahousing 152 forming an exterior thereof. In selected embodiments, ahousing 152 may have a substantially cylindrical shape or configuration.A housing 152 may include various sections. The sections may beseparable to facilitate assembly, repair, and the like.

In one embodiment, the various sections of a housing 152 may include abase 154, a lower section 156 resting on and extending upward from thebase 154, an intermediate section 158 resting on and extending upwardfrom the lower section 156, and an upper section 160 resting on andextending upward from the intermediate section 158. An upper section 160may include a feedstock inlet 162. A feedstock inlet 162 may beconnected to a conveyer system 144 to receive feedstock 16 therefrom. Alower section 156 may include a gas outlet 164 through which the syn-gasis extracted. It may also include a waste outlet 166 through which thewaste remaining after the gasification process is expelled from thegasifier 14.

In certain embodiments, a gasifier 14 may include a shaft 168 extendingvertically through the housing 152. Rotation of the shaft 168 may causerotation or motion of various components and contents contained withingasifier 14, promoting effective and efficient operation. One or moremotors 170 may be connected and positioned to urge rotation of the shaft168 about a vertical axis. For example, in one embodiment, a first motor170 a may be positioned proximate an upper end of the shaft 168, while asecond motor 170 b may be positioned proximate a lower end of the shaft168. The first motor 170 a may urge rotation of a first transmissionmechanism 172 a, which in turn may urge rotation of the shaft 168.Similarly, the second motor 170 b may urge rotation of a secondtransmission mechanism 172 b, which in turn may urge rotation of theshaft 168.

A gasifier 14 may include various ports 173, apertures 173, probes 173and the like. Such components 173 may support delivery or injection ofgases to locations within the gasifier 14. They may also support variouswires, sensors, and the like requiring access to the internal workingsof a gasifier 14.

In selected embodiments, a gasifier system 138 may include a wastesystem 174. A waste system 174 may conveyor the waste remaining afterthe gasification process away from a gasifier 14. In certainembodiments, a waste system 174 may include a motor 176, a conduit 178,and an auger positioned within the conduit 178. The conduit 178 mayextend from the gasifier 14 to a container 180 for housing the waste.The motor 176 may urge rotation of the auger within the conduit 178,thereby propelling the waste from one end of the conduit 178 (e.g., theend near the gasifier 14) to the other (e.g., the end near the container180). In selected embodiments, a container 180 may be mounted on wheels182, facilitating transport of the waste contained therein.

A gasifier system 138 may include a control system controlling one ormore systems (e.g., subsystems) associated with a gasifier system 138.In selected embodiments, the various components of a control system maybe housed in a control box 184. In one embodiment, a control box 184 maybe secured to a frame 186 supporting a hopper 142. Such an arrangementmay provide a gasifier system 138 that is modular in nature and iseasily transported.

Referring to FIG. 5, a control system 188 in accordance with the presentinvention may provide for manual control, automated control, or combinedmanual and automated control. For example, manual switches may controlcertain functionality, while programmed logic may control otherfunctionality. Still other functionality may be controlled by automatedsystems that are not computer based (e.g., fuses, circuit breakers, andthe like).

In selected embodiments, a control system 188 may include a computer190. A computer 190 may include a processor 192 or CPU 192. The CPU 192may be operably connected to a memory device 194. A memory device 194may include one or more devices such as a hard drive or othernon-volatile storage device, a read-only memory (ROM), and a randomaccess (and usually volatile) memory (RAM or operational memory). Suchcomponents 192, 194 may exist in a single node or may exist in multiplenodes remote from one another.

In selected embodiments, a computer 190 may include an input device 196for receiving inputs from a user or from another device. Input devicesmay include one or more physical embodiments. For example, a keyboardmay be used for interaction with the user, as may a mouse, stylus pad,switch, or button (e.g., emergency stop button). A touch screen, atelephone, or simply a telecommunications line, may be used forcommunication with other devices, with a user, or the like. Similarly, ascanner may be used to receive graphical inputs, which may or may not betranslated to other formats. A hard drive or other memory device may beused as an input device whether resident within the particular node orsome other node connected by a network 198. In selected embodiments, anetwork card 200 (interface card) or port 202 may be provided within anode to facilitate communication through such a network 198.

In certain embodiments, one or more output devices 204 may be providedwithin a node, or accessible within the computer 190. Output devices 204may include one or more physical hardware units. For example, ingeneral, one or more ports 202 (e.g., USB ports) may be used to acceptinputs into and send outputs from the computer 190. Nevertheless, amonitor may provide outputs to a user for feedback during a process, orfor assisting two-way communication between the processor 192 and auser. A printer, a hard drive, buzzer or alarm, lights, or other devicesmay be used for to output information and may be considered outputdevices 204 in accordance with the present invention.

Internally, a bus, or plurality of buses, may operably interconnect theprocessor 192, memory devices 194, input devices 196, output devices204, network card 200, and ports 202. The bus may be thought of as adata carrier. As such, the bus may be embodied in numerousconfigurations. Wire, fiber optic line, wireless electromagneticcommunications by visible light, infrared, and radio frequencies maylikewise be implemented as appropriate for the bus and the network 198.

In general, a network 198 to which a computer 190 connects may, in turn,be connected through a router to another network. In general, variouscomponents of a computer 190 may be on the same network, adjoiningnetworks (i.e., network and neighboring network), or may be separated bymultiple routers and multiple networks as individual nodes on aninternetwork. The individual nodes may have various communicationcapabilities. In certain embodiments, a minimum of logical capabilitymay be available in any node or computer 190. For example, each node maycontain a processor 192 with more or less of the other componentsdescribed hereinabove.

A network 198 may include one or more servers. Servers may be used tomanage, store, communicate, transfer, access, update, and the like, anypractical number of files, databases, or the like for other nodes orcomputers 190 on a network 198. Typically, a server may be accessed byall nodes on a network 198. Nevertheless, other special functions,including communications, applications, directory services, and thelike, may be implemented by an individual server or multiple servers.

In general, a node or computer 190 may need to communicate over anetwork 198 with a server, a router, or other nodes. Similarly, a nodemay need to communicate over another neighboring network in aninternetwork connection with some remote node. Likewise, individualcomponents may need to communicate data with one another. Acommunication link may exist, in general, between any pair of devices.

One or more software programs running on a computer 190 may controlvarious systems (e.g., subsystems) of a gasifier system 138. The varioussystems controlled by a control system 188 may largely be divided intotwo classes, namely feedback systems 206 and implementations systems208. Through the feedback systems 206, a control system 188 may learnwhat is happening within the gasifier 14 or other components of thegasifier system 138. Through the implementation systems 208, a controlsystem 188 may effect changes to the operation of the gasifier system138, sound an alarm, or the like.

Referring to FIG. 6, in selected embodiment, a sensor suite 210 may bethe primary feedback system of a control system 188 in accordance withthe present invention. Within a sensor suite 210 may be temperaturesensors 212, pressure sensors 214, flow meters 216, oxygen sensors 218,nitrogen sensors 220, carbon dioxide sensors 222, current sensors 224,resistance sensors 226, fill-level sensors 228, rotational speed sensors230, and the like 232. By closely monitoring the outputs of the varioussensors of the sensor suite 210, a control system 188 may implementchanges as necessary to maintain the gasifier 14 operating at or nearpeak efficiency.

In certain embodiments, the core of a sensor suite 210 may be thetemperature sensors 212 sensing or measuring the temperature of manylocations within a gasifier system 138. In selected embodiments, thetemperature sensors 212 may include thermocouples, each outputting asignal or current corresponding to the temperature thereof.

In selected embodiments, pressure sensors 214 may provide feedback onthe effectiveness of a vacuum pump 150 by monitoring the pressure in theconduit 148 of a feed system 140, as well as in the upper section of agasifier 14. Flow meters 216 may measure the flow of gas (e.g., oxygen,oxygen enriched air, air) into a gasifier 12, as well as the flow of gas(e.g., syn-gas) out of a gasifier 14. Oxygen, nitrogen, and carbondioxide sensors 218, 220, 222 may be positioned to monitor thecomposition of the air within the upper section 160 or gas outlet 164 ofa gasifier 14. Current and resistance sensors 224, 226 (e.g., fuses,breaker switches, etc.) may monitor the electrical characteristics ofcertain components in an effort to identify problems.

One or more fill-level sensors 228 may be positioned to monitor the flowof material through a gasifier system 138. For example, a fill-levelsensor 228 (FIG. 4) may be positioned to monitor the amount of feedstock16 contained within a hopper 142. A control system 188 may use the dataprovided by the fill-level sensor 228 to determine when more feedstock16 should be added to a hopper 142 or when the hopper 142 is full.Similar sensors 228 may be positioned within the upper section 160 of agasifier 14, within the container 180 of the waste system 174, and thelike. Accordingly, a control system 188 may learn when more feedstock 16needs to be added to a gasifier 14, when a container 180 needs to beemptied, and the like.

In selected embodiments, one or more rotational sensors 230 may monitorthe speed of rotation of certain mechanisms such as the shaft 168extending through the gasifier 14. Accordingly, the control system 188may ensure that the feedstock 16 and the like with the gasifier 14 arebeing mixed or agitated sufficiently.

A control system 188 may include a heater suite 234. For example, acontrol system 188 may include one or more heaters 236 (e.g., electricalresistance heaters 236 converting electrical current into heat). Eachsuch heater 236 may be coupled to a heater controller 238 (e.g.,controlling the current delivered to that heater 236). The heaters 236of a heater suite 234 may be positioned within a gasifier 14 and providea control system 188 the ability to increase the temperature of specificlocations within that gasifier 14.

A control system 188 may include a gas-delivery system 240. In selectedembodiments, a gas-delivery system 240 may deliver one or more gassessuch as oxygen, oxygen enriched air, air, nitrogen, and the like to agasifier 14. A gas-delivery system 240 may include one or more sources242 (e.g., tanks, pumps, or the like) of gas operably connected to ports244 delivering the gas to specific locations within a gasifier 14.Between a source of gas 242 and a port 244 may be a proportional controlvalve 246 operating under the direction or control of a proportionaldriver 248. Accordingly, a control system 188 may proportionally controldelivery of gas.

In selected embodiments, a gas-delivery system 240 may perform twofunctions. The first may be delivery of oxygen to the gasifier 14. Iftoo much is added, temperatures within the gasifier 14 may riseundesirably and the gasifier 14 may support more complete combustionthan generation of syn-gas. Conversely, if insufficient oxygen is added,the temperature may decrease and oxygen may become the limiting reactantin the generation of syn-gas.

A second function of a gas-delivery system 240 may be to facilitate shutdown (e.g., emergency shut down) of a gasifier 14. In selectedembodiments, a gas-delivery system 240 may participate in such processesmy cutting off oxygen to the gasifier 14, purging the oxygen from agasifier 14 by flooding the gasifier 14 with nitrogen (or some other gasthat does not support combustion), or some combination thereof. Inselected embodiments, a three-way valve may connect a source 242 ofcombustion-supporting gas or gasses, a source 242 of combustion-stoppinggas or gasses, and the various ports 244. Accordingly, operation of thethree-way valve may determine whether a gas-delivery system 240 aidscombustion or stops it.

In certain embodiments, a control system 188 may include a coolingsystem 250. A cooling system 252 may remove heat from various structuresor flows of a gasifier system 138. For example, a cooling system 252 mayinclude a heat exchanger 252 transferring heat from the syn-gas exitinga gasifier 14 to a coolant 254. In selected embodiments, a coolingsystem 250 may include a heat exchanger 252 taking the form of a coolingjacket 252 encircling the lower section 156 of a gasifier 14. Coolant254 may be circulated through the jacket 252 to remove heat from thelower section 156. In selected embodiments, a cooling system 250 mayinclude a circulation pump 256 to circulate the coolant 254.

As set forth hereinabove, a gasifier system 138 in accordance with thepresent invention may include a feed system 140, waste system 174, andvacuum pump 150. In selected embodiments, these systems 140, 174 andcomponents 150 may be considered part of a control system 188.Specifically, the motive elements thereof (motors 146, 176, 170 a, 170b, 150) may operate as part of, or under the direction of, a controlsystem 188.

In selected embodiments, a control system 188 may include one or morefans 258 or fan motors 258. For example, a control system 188 mayinclude a fan 258 for extracting or pumping syn-gas out the gas outlet164 of a gasifier 14. A control system 188 may also include one or morecooling fans 258 (e.g., fans 258 circulating air through a control box184 or some subset or portion thereof.

A control system 188 may include other 260 systems as desired ornecessary to aid in the efficient and safe operation of a gasifiersystem 138 in accordance with the present invention.

Referring to FIGS. 7 and 8, in selected embodiments, a gasifier 14 inaccordance with the present invention may be a downdraft gasifier 14.Accordingly, the general flow of gases in the gasifier 14 may bedownward.

A gasifier 14 may heat feedstock 16 (e.g., pre-processed feedstock) to atemperature where it is converted to syn-gas. Feedstock 16 may enterthrough a feedstock inlet 162 and travel down through the gasifier 14toward a waste outlet 166. A fan 258 may draw hot syn-gas out of thegasifier 14 through the gas outlet 164. The fan 258 may further propelthe syn-gas into a cyclone separator and one or more heat exchangers252. A heat exchanger 252 may harvest the heat from the gasifier 14 anduse it to make steam for driving a turbine 112. The cyclone separatormay separate the syn-gas from any ash that it may be carrying that wasnot removed by the slag forming proximate the lower portions of agasifier 14.

In selected embodiments, a gasifier 14 in accordance with the presentinvention may include four zones that function in unison tosimultaneously process the feedstock 16 and generate clean syn-gas.These zones are the drying zone 262, tar-formation zone 264, oxidationzone 266, and reduction zone. In a drying zone 262, the feedstock 16 isstored for consumption. Also, heat radiating upward from a lower,oxidation zone 266 may drive off the residual moisture as water vapor.The water vapor may participate in the chemical reactions in thereduction zone when carbon reacts with the water vapor to generatecarbon monoxide and hydrogen (H₂), the desired output.

Because the tar-formation zone 264 is closer to the oxidation zone 266than the drying zone 262, the temperature within a tar-formation zone264 may be higher than that within the drying zone 262. In thetar-formation zone 264, the feedstock 16 may be heated without oxygen toproduce oil, tar, char, and charcoal. These products may provide a readysupply of carbon for the chemical reactions that later occur in thereduction zone.

In the oxidation zone 266, all or part of the volatile materials may beoxidized to generate the heat for the chemical reactions of the process.At the conclusion of the oxidation zone 266 or as the material passesout of the oxidation zone 266, approximately 20% to 30% of the organicmaterial may have been oxidized and the oxygen is typically consumed.Accordingly, there is typically no flame in the succeeding, reductionzone. Some combustible gases may be generated in the oxidation zone 266.

In the reduction zone, the hot gases generated in the oxidation zone 266may react with the carbonaceous material generated in the tar-formationzone 264 to convert most of the material to syn-gas, which comprisesprimarily carbon monoxide and hydrogen. During these reactions thesensible heat or heats of the chemical reactions are converted intochemical energy for the syn-gas. This, being endothermic, may result incooling of the mass to below 800° C., which effectively stops thechemical processes and no further syn-gas is typically formedthereafter.

In the high temperatures of this process, the residual inert ash meltsto a molten slag. This slag may impart a scrubbing and filtering actionon the syn-gas produced. This may strip the gas of most all of theimpurities and solid particles. The binders incorporated duringpreprocessing of the feedstock 16 may trap pollutants within the slag.The slag may have the consistency of sand and may be safely used as anaggregate or deposited in a landfill. For this reason the syn-gasgenerated within a gasifier 14 in accordance with the present inventionmay be used directly without “hot gas cleanup.”

In selected embodiments, a gasifier 14 may include an enclosed top 270.The enclosed top 270 may stop all or some portion of the atmosphericnitrogen from entering a gasifier 14 and generating undesirablecompounds. Also, the enclosed top 270 may assist in maintaining thedesired temperatures within the gasifier 270. In certain embodiments,the top 270 of a gasifier 14 may include one or more pressure reliefvalves or vents to prevent excessive pressurization of the gasifier 14.

In certain embodiments, a refractory stack 272 may be housed within theintermediate section 158 of a gasifier 14. A refractory stack 272 may beformed as a single, monolithic unit. Alternatively, a refractory stack272 may include a plurality of sections. In selected embodiments, arefractory stack 272 or the various sections thereof may be formed of aheat resistant material. For example, they may be formed of ceramic orrefractory.

A refractory stack 272 may improve the heat retention, durability, andlife span of a gasifier 14. The various sections forming a refractorystack 272 may be replaced as needed, without requiring the replacementof the remaining structures of the gasifier 14. Accordingly, the housing152 of a gasifier 14 in accordance with the present invention may beformed in separable horizontal sections 154, 156, 158, 160, facilitatingaccess to the refractory stack 272 (and other internal components) of agasifier 14. In certain embodiments, the housing 152 of a gasifier 14may also include separable vertical sections in the oxidation andreduction zones, further facilitating maintenance or replacement of thesections of a refractory stack 272.

The number of sections in a refractory stack 272 may vary betweenembodiments. In one embodiment, a refractory stack 272 may include fivesections, namely, a lower manifold 274, a lower intermediate section276, a middle intermediate section 278, an upper intermediate section280, and an upper manifold 282. The lower intermediate section 276 mayrest on and extend upward from the lower manifold 274. The middleintermediate section 278 may rest on and extend upward from the lowerintermediate section 276. The upper intermediate section 280 may rest onand extend upward from the middle intermediate section 278. The uppermanifold 282 may rest on and extend upward from the upper intermediatesection 280. The interior of an upper manifold 282 may define thetar-formation zone 264. The interior of a lower manifold 274 may definethe reduction zone.

A shaft 168 in accordance with the present invention may be formed ofany suitable material. Suitable materials may include metals, ceramics,and the like. In one embodiment, a shaft 168 may form a conduit. Coolant254 from a cooling system 250 may be circulated through the shaft 168 tomaintain the shaft 168 within an acceptable temperature range.

In certain alternative embodiments, a gasifier 14 in accordance with thepresent invention may include two independent center shafts 168. One mayextend down from the top of the gasifier 168, while the other extends,coaxially therewith, up from the bottom. Each shaft 168 may be driven bya different motor 170 a, 170 b. Accordingly, the shafts 168 may berotated at different speeds, facilitating independent optimization ofthe mixing within the upper portions 160, 282 of a gasifier 14 and theagitation within the lower portions 156, 274 of the gasifier 14. Also,in such an embodiment, neither shaft 168 may extend through theoxidation zone 266, the hottest portion of the gasifier 14. This maypermit the shafts 168 to be formed of materials having less tolerance toheat, which may be less expensive and more readily available.

In selected embodiments, a gasifier 14 may include a mixing blade 284connected to rotate with the shaft 168. In one embodiment, a mixingblade 284 may be positioned within both the upper section 160 and theupper manifold 282. Accordingly, as the shaft 168 rotates about avertical axis, the mixing blade 284 may mix the contents (e.g.,pre-processed feedstock) of the upper section 160 and upper manifold282. This mixing may improve the distribution of heat rising from theoxidation zone 266, thereby improving the drying and tar formationeffects. In selected embodiments, the mixing blade 284 may scrape thecontents of the upper manifold 282 away from an interior surfacethereof. This may remove any dead or stagnant zones where the feedstock16 may collect and not continue on down to the oxidation zone 266.

Certain sections of a refractory stack 272 may include multipleapertures extending vertically therethrough. For example, in oneembodiment, the lower intermediate, middle intermediate, upperintermediate, and upper manifold sections 276, 278, 280, 282 may eachinclude multiple apertures extending vertically therethrough. Inselected embodiments, these apertures may be aligned between the varioussection 276, 278, 280, 282 to form multiple columnar cavities 286. Eachcolumnar cavity 286 may extend from the upper manifold 282 to the lowermanifold 274, placing the upper manifold 282 in communication with thelower manifold 274.

Each columnar cavity 286 of a gasifier 14 in accordance with the presentinvention may act as an independent oxidation zone 266. Accordingly, agasifier 14 may provide parallel paths for feedstock 16 passingtherethrough. Furthermore, each columnar cavity 286 may have a widththat is less than its height. For example, in selected embodiments, acolumnar cavity 286 in accordance with the present invention may have anaspect ratio (i.e. width divided by height) of about 0.40 to about 0.22.This may increase the time the feedstock 16 spends in the oxidation zone266, increasing the amount of oxidation that occurs. Moreover, eachcolumnar cavity 286 may have a dedicated heater 236, dedicated gas ports244, and dedicated temperature sensors 212.

These heaters 236, ports 244, and sensors 212 may be positioned withinor proximate the apertures defining the columnar cavities 266. Thus, thenarrowness of the cavities 266 and the positioning of the heaters 236,ports 244, and sensors 212 may shorten the distance between feedbacksystems 206, implementation systems 208, and the feedstock 16.Accordingly, a control system 188 may individually, rapidly, andprecisely control the environment within each columnar cavity 266.

In selected embodiments, the various apertures in the various sections276, 278, 280, 282 that align to form the columnar cavities 286 may notbe exactly cylindrical. For example, the apertures in selected sections278, 280 may be conical in shape, converging somewhat when viewed withrespect to the downward flow of the feedstock 16. In another section276, the apertures may converge then diverge.

Apertures so configured may perform two functions. First, they maycumulatively create a columnar cavity 286 that varies in width along itsheight. This may induce some motion or agitation within the feedstock 16as is moves down through the cavity 286. Additionally, apertures soconfigured may create one or more lips 288 or overhangs 288 within thecolumnar cavities 286.

In selected embodiments, these overhangs 288 may extend thecircumference of the cavities 286. Tucked on the underside of theoverhangs 288 may be grooves 290. These grooves 290 may also extend thecircumference of the cavities 286. The grooves 290 may be completelyexposed, partial exposed, or substantially covered by the section 276,278, 280 positioned immediately therebelow. Certain grooves 290 (e.g.,those that are partially exposed or substantially covered) may be usedas distribution channels, distributing the gas delivered by a port 244around a circumference of a cavity 286. Others 290 may house and protecta heater 236. Accordingly, a heater 236 (e.g., resistance heater 236)may extend circumferentially around a columnar cavity 286.

In certain embodiments, heaters 236 may be positioned proximate theupper portions of a columnar cavity 286. The heaters 236 may providegreater control in initiating and automating the gasification process.Additionally, the heaters 236 may reduce the amount of time required tobring a gasifier 14 into optimal production.

That is, gasifiers 14 often emit the most pollution (e.g., “dirtiest”syn-gas) at startup, before the temperatures of the different zones 262,264, 266 have reached their target ranges. Adding heaters 236 mayprovide sources of heat that are independent of the combustion of thefeedstock 16 and completely within the control of a control system 14.Thus, the amount of time spent emitting the startup flair may beminimized. Additionally, in selected embodiments, a catalytic oxidizermay be applied to the exhaust of a startup flair. This may ensure thatundesirable products do not escape the gasifier 14 before it is runningin its optimal, efficient, and “clean” temperatures.

In selected embodiments, a grate 292 may be positioned within a gasifier14 to form the bottom boundary of the reduction zone. In oneembodiments, a grate 292 may be positioned proximate the underside of alower manifold 274. A lower manifold may include an aperture 294extending vertically therethrough. The aperture 294 may have anundulating perimeter (e.g., a perimeter that varies in and out in aradial direction along a path extending in a circumferential direction).A plurality of balls 296 (e.g., ceramic balls about ½ inch in diameter)may be supported by the grate 292 and held by the grate 292 within theaperture 294 of the lower manifold 274.

A grate 292 may be supported and held in position by a grate support298. A grate support 298 may be connected to rotate with a shaft 168.Rotation of the grate support 298 may result in rotation of the grate292, which in turn may result in rotation of the balls 296. Because anaperture 294 having an undulating perimeter laterally contains the balls296, relative rotation between the balls and the aperture may result inagitation or mixing of the balls 296. The resultant bed of moving andmixing balls 296 may provide a semi permeable barrier, permittingsyn-gas and small particles to work their way through, while blockingthe passage of larger particles. Thus, only feedstock 16 that has beensufficiently oxidized and reduced may exit the reduction zone.

In selected embodiments, vibrators (e.g., magnetic vibrators) may beapplied to agitate a grate 292 within a gasifier 14. The vibrators mayfacilitate and improve flow through the gasifier 14. Additionally, agrate 292 may be formed with various apertures extending therethrough.The balls 296 may be deposited on top of the grate. The vibrators mayprevent the balls 296 from settling into and blocking the apertures inthe grate 292.

In certain embodiments, a gasifier 14 may include one or more wiperblades 300 positioned with the lower section 156. A wiper blade 300 maybe connected to rotate with the shaft 168. In one embodiment, one ormore wiper blades 300 may be formed as part of, or be connected to, agrate support 298. Accordingly, as the grate support 298 rotates, so mayone or more wiper blades 300. A wiper blade 300 may urge the contents ofthe lower section 156 toward the ash outlet 166. In selectedembodiments, one or more wiper blades 300 may rotate across (e.g.,scrap) the floor 302 of a lower section 156.

A second wall 304 applied to the lower section 156 of a gasifier 14 mayform a heat exchanger 252 or cooling jacket 252. Coolant 254 circulatedthrough the interior cavities 306 formed by the second wall 304 mayremove heat from the lower section 156 and its contents. Accordingly,the temperature within the lower section 156 may be controlled toprotect the material forming the lower section 156 from overheating,prepare the residue for disposal, or the like.

A lower section 156 in accordance with the present invention may includea separation wall 307. A separation wall 307 may provide a barrierbetween particles falling through a grate 292 and a gas outlet 164. Thismay reduce the number of particles that leave the lower section 156entrained within the syn-gas.

Referring to FIG. 9, the upper section 160 of a gasifier 14 inaccordance with the present invention may be formed of any suitablematerial in any suitable manner. In selected embodiments, an uppersection 160 may be formed of metal and include a tubular structure 308supported by external ribs 310. The tubular structure 308 may includeone or more apertures 312 permitting entrance of sensors, feeds, or thelike into the upper section 160. In one embodiment, six sensors 212 mayeach monitor a different zone within the upper section 160. One or moreoxygen sensors 218, nitrogen sensors 220, and carbon dioxide sensors 222may also monitor the contents of the upper section 160.

Referring to FIG. 10, an intermediate section 158 may be formed of anysuitable material. In selected embodiments, an intermediate section 158may be formed as a tubular metal construct. Various apertures 314 mayextend through the intermediate section 158. Such apertures 314 mayprovide locations for sensors 210, sensors wires, and the like to enterthe intermediate section 158. In one embodiment, an intermediate section158 may include one aperture 314 for each columnar cavity 286 of therefractory stack 272 to be housed therein.

Referring to FIG. 11, in selected embodiment, an aperture cover 316 maybe applied to each aperture 314 extending through an intermediatesection 158. An aperture cover 316 itself may include one or moreapertures 318 or ports 318 for receiving, securing, and sealing aroundone or more sensors 210, sensors wires, and the like. In one embodiment,the apertures 318 in an aperture cover 316 may accommodate or secure oneheater 236, one heater temperature sensor 212 monitoring the temperatureat or near the heater 236, four cavity temperature sensors 212 (eachcorresponding to a different section 274, 276, 278, 280 of a particularcolumnar cavity 286), and two gas-delivery ports 244 (each correspondingto a different section 278, 280 of a particular columnar cavity 286).

Referring to FIG. 12, a lower section 156 may secure to a base 154. Inselected embodiments, a lower section 156 may include one or moreapertures 318 or ports 318 for receiving, securing, and sealing aroundone or more sensors 210, sensors wires, and the like. For example, inone embodiment, a lower section 156 may include three ports 318 spacedcircumferentially around an upper portion of the lower section 156.Sensors 212 placed at those locations may monitor the temperate of thegas exiting the reduction zone. One or more apertures 318 or ports 318may be positioned proximate a gas outlet 164, providing a location forsecuring a temperature sensor 212, flow meter 216, oxygen sensor 218,and the like.

In certain embodiments, a lower section 156 may include an upper plate320 extending circumferentially around the top of thereof. Whenassembled, the upper plate 320 may provide the vertical support for therefractory stack 272. In one embodiment, one or more alignment pins 322may extend upward from the upper plate 320. These pins 322 may beinserted within corresponding apertures within the lower manifold 274,thereby ensuring a proper alignment. In selected embodiments, the pins322 may have internal apertures that are threaded to receive a threadedrod, clamping the refractory stack 272 together and down against theupper plate 320.

Referring to FIG. 13, a top 270 of a gasifier 14 may be formed of anysuitable material in any suitable manner. In selected embodiments, a top270 may include one or more mounts 324 for receiving and securing atransmission mechanism 172 or motor 170. A top 270 may also include ashaft mount 326 for securing or locating a shaft 168. A top 270 may alsoinclude one or more apertures 318 or ports 318 for receiving, securing,and sealing one or more sensors 210 (e.g., pressure sensors 214, oxygensensors 218, nitrogen sensors 220, carbon dioxide sensors 222, and thelike). In one embodiment, a top 270 may include a connector 328 forpassing gas in or out of a gasifier 14. For example, in one embodiment,a connector 328 may be a location for nitrogen (or some othernon-combustion support gas) infusion into a gasifier 14. Alternatively,a connector 328 may provide a location for securing a pressure releasevalve.

Referring to FIG. 14, in selected embodiments, a gasifier 14 may includea bottom 330 secured at the lower portion or extreme of a lower section156. In selected embodiments, a bottom 330 may include a waste outlet166, one or more apertures 318 or ports 318 for receiving, securing, andsealing sensors 210 or the like, one or more mounts 324 for receivingand securing a transmission mechanism 172 or motor 170, a shaft mount326 for securing or locating a shaft 168, and the like.

Referring to FIG. 15, a mixing blade 284 in accordance with the presentinvention may be formed of any suitable material. In selectedembodiments, a mixing blade 284 may be formed of metal. A mixing blade284 may include an aperture 332 for receiving a shaft 168 therethrough.A mixing blade 284 may also include a perimeter 334 contoured to matchthe shape of the container (e.g., upper section 160, upper manifold 282)in which it will rotate, thereby ensuring efficient and complete mixing.In selected embodiments, a mixing blade 284 may also include one or moredeflectors 336 to increase or enhance the mixing effect produced.

Referring to FIGS. 16 and 17, in selected embodiments, a grate 292 mayinclude a plurality of apertures 338 extending vertically therethrough.The apertures 338 may be sized smaller than the balls 296 that may besupported by the grate 292. In one embodiment, the apertures 338 may becircular. A grate 292 may also include an aperture 340 for receiving ashaft 168 therethrough.

In selected embodiments, a grate support 298 may include a platform 342.In one embodiment, a platform 342 may include a circumferentiallyextending rim 344 connected to radially extending ribs 346. The ribs 346may be connected to a central column 348. A column 348 may provide ashield for a shaft 168 extending therethrough against the contents ofthe lower section 156 of a gasifier 14. A column 348 may also space theplatform 342 a desired distance from the floor 302 of a lower section156. In selected embodiments, one or more wiper blades 300 may connectto the lower portion of a column 348 and extend substantially radiallyaway therefrom.

Referring to FIGS. 18 and 19, a gasifier 14 in accordance with thepresent invention may be scaled to provide a desired throughput. Arefractory stack 272 may also be scaled to provide a desired throughput.Additionally, the various components 274, 276, 278, 280, 282 may besized to support fabrication in a ceramic or refractory material. Thenumber of columnar cavities 286 may vary with the size of a refractorystack 272. In general, the larger (e.g., wider) the stack 272, the morecolumnar cavities 286 may be included.

In certain embodiments, an upper manifold 282 in accordance with thepresent invention may include an upper rim 350, a base plate 352, and asidewall 354 converging somewhat as it extends from the upper rim 350 tothe base plate 352. An upper rim 350 may include one or more apertures356 extending vertically therethrough. The apertures 356 may beconfigured to align with and engage pins extending downward from a lowerportion of an upper section 160. Alternatively, the apertures 356 mayreceive a threaded rod extending to engage the pins 322 on a lowersection 156, clamping the refractory stack 272 together and down againstthe upper plate 320 of the lower section 156.

In selected embodiments, a base plate 352 may include multiple apertures358, 360 extending vertically therethrough. One aperture 358 may becentrally located and sized to receive a shaft 168 extendingtherethrough. The other apertures 360 may form part of the variouscolumnar cavities 286.

The underside of a base plate 352 may include various grooves 290. Forexample, the underside of a base plate 352 may include grooves 290 a forreceiving heaters 236 therein. The grooves 290 a may extend around thecircumference of the apertures 360. Accordingly, heaters 236 placedwithin such grooves 290 a may distribute heat circumferentially around acolumnar cavity 286. Other grooves 290 b may provide locations fortemperature sensors 212 to extend and monitor the temperature ofcorresponding heaters 236.

The underside of a base plate 352 may also include various recesses 362.Selected recesses 362 a may be sized and positioned to engage extensionsextending from a neighboring section 280. Accordingly, such recesses 362a may provide a mechanism for aligning the various sections 274, 276,278, 280, 282 of a refractory stack 272. Other recesses 362 b may besimply be hallowed out portions of various shapes. Such recesses 362 bmay lower the amount of material required to form the section 274, 276,278, 280, 282, reduce the weight of the section 274, 276, 278, 280, 282,reduce the thermal mass of the section 274, 276, 278, 280, 282, or thelike. In selected embodiments, the exterior of a sidewall 354 may alsoinclude recesses 362 b for material savings, weight savings, and areduction in thermal mass.

Referring to FIGS. 20 and 21, in selected embodiments, a refractorystack 272 may include repeated sections 278, 280. That is, a refractorystack 272 may include sections 278, 280 that are substantially identicalto one another. For example, in the illustrated embodiment, the middleintermediate section 278 and the upper intermediate section 280 of arefractory stack 272 are substantially identical. In certainembodiments, repeating sections 278, 280 may be added or taken away toincrease or decrease, respectively, the length of the columnar cavities286 and, therefore, the corresponding oxidations zones 266.Additionally, use of repeated section 278, 280 may lower manufacturingcosts and reduce part inventories.

A section 274, 276, 278, 280 in accordance with the present inventionmay include one or more extensions 364 extending upward therefrom. Suchextensions 364 may be sized and positioned to engage correspondingrecesses 362 a located in an underside of neighboring sections 276, 278,280, 282. A section 278, 280 may also include multiple grooves 290extending from the perimeter to encircle an aperture 360. In selectedembodiments, such grooves 290 may facilitate delivery and distributionof gas to a corresponding columnar cavity 286.

In selected embodiments, the perimeter of a section 278, 280 inaccordance with the present invention may be substantially circular.Alternatively, the perimeter may include periodic recesses 364 b andtake on a star-like shape. Similarly, in some embodiments, a shaftaperture 358 may be circular. Alternatively, in other embodiments, ashaft aperture 358 may be somewhat star-shaped. Such as shape may reducematerial usage, reduce weight, lower thermal mass, and reduce the rateof heat transfer between the section 274, 276, 278, 280, 282 and theshaft 168.

In certain embodiments, an aperture 366 may extend from the perimeter ofa section 274, 276, 278, 280 radially inward to intersect with anaperture 360 forming part of a columnar cavity 286. Such an aperture 366may provide a sensor (e.g., a temperature sensor 212) access to thecolumnar cavity 286.

Referring to FIGS. 22 and 23, in selected embodiments, the apertures 360extending vertically through a lower intermediate section 276 of arefractory stack 272 may have a cross-section that varies along thelength of the aperture 360. For example, in one embodiment, theapertures 360 may converge then diverge, when viewed with respect to thedownward flow of the feedstock 16 through the gasifier 14.

A lower intermediate section 276 in accordance with the presentinvention may include a collar 368 extending downward therefrom. Whenassembled, a collar 368 may extend downward to contact a grate 292. Inselected embodiments, a collar 368 may shield a shaft 168 extendingtherethrough from the temperatures and contents of the interior of alower manifold 274 (i.e., the reduction zone).

Referring to FIGS. 24 and 25, a lower manifold 274 may include anaperture 294 extending vertically therethrough. In selected embodiments,the perimeter 370 of the aperture 294 may undulate, varying in and outin a radial direction along a path extending in a circumferentialdirection. When assembled, an aperture 294 of a lower manifold 274 maycombine with the collar of a lower intermediate section 276 to form anannular region. Balls 296 supported by a grate 292 may define the floorof the annular region. Accordingly, when the grate 292 rotates with theshaft 168, the balls 296 may be mixed somewhat as they circulate aroundthe annular region.

A lower manifold 274 in accordance with the present invention mayinclude a shoulder 372. A shoulder 372 may extend circumferentiallyaround a lower portion of the manifold 274. A shoulder 372 may provide abase suitable for supporting a refractry stack 272 on the upper plate320 of a lower section 156 of a gasifier 14. In selected embodiments, ashoulder 372 may include one or more apertures sized and positioned toengage the pins 322 extending from an upper plate 320, ensuring a properand secure alignment therebetween.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrative,and not restrictive. The scope of the invention is, therefore, indicatedby the appended claims, rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A method comprising: selecting a downdraft gasifier comprising: ahousing, a refractory stack contained within the housing and comprisinga plurality of sections formed of refractory, the plurality of sectionscomprising a lower manifold, at least one intermediate section restingon and extending upward from the lower manifold, and an upper manifoldresting on and extending upward from the at least one intermediatesection, and the refractory stack wherein the upper manifold and the atleast one intermediate section each comprise a plurality of aperturesextending vertically therethrough, the plurality of apertures of theupper manifold aligning with the plurality of apertures of the at leastone intermediate section to form a plurality of columnar cavities, eachextending from the upper manifold to the lower manifold and placing theupper manifold in communication with the lower manifold; placing afeedstock into the upper manifold; measuring the temperature of eachcolumnar cavity of the plurality of columnar cavities; and adjusting theflow of at least one gas selected from the group consisting of oxygen,oxygen enriched air, and air to a particular columnar cavity to maintainthe temperature of the particular columnar cavity within a particularrange.
 2. The method of claim 1, wherein adjusting comprises increasingthe flow of the at least one gas to raise the temperature of theparticular columnar cavity and decreasing the flow of the at least onegas to lower the temperature of the particular columnar cavity.
 3. Themethod of claim 1, wherein the downdraft gasifier further comprises ashaft system comprising at least one motor and a shaft, the shaftextending vertically through the housing, the at least one motorconnected to rotate the shaft about an axis extending vertically.
 4. Themethod of claim 3, further comprising rotating, by the at least onemotor, the shaft about the axis extending vertically.
 5. The method ofclaim 4, wherein the downdraft gasifier further comprises a mixing bladeconnected to rotate with the shaft and mix the contents of the uppermanifold.
 6. The method of claim 5, further comprising scraping, by themixing blade, the contents of the upper manifold away from an interiorsurface of the upper manifold.
 7. The method of claim 4, wherein thedowndraft gasifier further comprises at least one wiper blade connectedto rotate with the shaft.
 8. The method of claim 7, further comprisingurging, by the at least one wiper blade, the contents of the lowersection toward the ash outlet.
 9. The method of claim 4, wherein thelower manifold comprises an aperture extending vertically therethrough,the aperture having an undulating perimeter.
 10. The method of claim 9,wherein the downdraft gasifier further comprises a grate connected torotate with the shaft and positioned adjacent the lower manifold. 11.The method of claim 10, wherein the downdraft gasifier further comprisesa plurality of balls supported by the grate and held by the grate withinthe aperture of the lower manifold.
 12. The method of claim 11, furthercomprising agitating, by the undulating perimeter, the plurality ofballs as the grate rotates with the shaft.
 13. The method of claim 1,wherein the housing further comprises a base, a lower section resting onand extending upward from the base, an intermediate section resting onand extending upward from the lower section, and an upper sectionresting on and extending upward from the intermediate section, the lowersection comprising a gas outlet and a waste outlet, the upper sectioncomprising a feedstock inlet.
 14. The method of claim 13, wherein therefractory stack is housed with the intermediate section.
 15. The methodof claim 14, wherein placing the feedstock further comprises passing thefeedstock into the upper section through the feedstock inlet.
 16. Themethod of claim 15, further comprising extracting syn-gas out of thelower section through the gas outlet.
 17. The method of claim 1, whereinthe downdraft gasifier further comprises: a plurality of electricalresistance heaters, each delivering heat to at least one columnar cavityof the plurality of columnar cavities; a plurality of temperaturesensors, each outputting a signal corresponding to the temperature of atleast one columnar cavity of the plurality of columnar cavities; and aplurality of ports, each delivering at least one gas selected from thegroup consisting of oxygen, oxygen enriched air, and air to at least onecolumnar cavity of the plurality of columnar cavities.
 18. The method ofclaim 17, wherein the downdraft gasifier further comprises: a coolantsystem comprising coolant passing through a cooling jacket encirclingthe lower section; a feed system controlling passage of feedstock intothe upper section; an extraction system pulling gas out of the lowersection through the gas outlet; and a control system monitoring theoutput of each sensor of the plurality of temperature sensors andperforming the adjusting.
 19. The method of claim 1, further comprising:grinding municipal solid waste to produce a first output; mixing intothe first output at least one of a quantity of zeolite and a quantity ofdolomite to produce a second output; pelletizing the second output toform the feedstock.
 20. The method of claim 1, further comprising:starting the gasifier; wherein the downdraft gasifier further comprisesa plurality of electrical resistance heaters, each delivering heat to atleast one columnar cavity of the plurality of columnar cavities; andwherein starting comprises delivering, before the placing, sufficientcurrent to each heater of the plurality of electrical resistance heatersto raise the temperate of each columnar cavity of the plurality ofcolumnar cavities into the particular range.